Failed tests:
LabelUnderlineTest.testLabelsUnderline:76 Images are visibly different, found 10686 different pixels, against a threshold of 1200
You can add -Dorg.geotools.image.test.interactive=true to show a dialog comparing them (requires GUI support)

I suspect that in underlineStyle.sld:

<CssParameter name="font-family">Vera</CssParameter>

should be

<CssParameter name="font-family">Bitstream Vera Sans</CssParameter>

as in all the other tests using Vera.ttf. The reference output also needs to be updated.